Some engines utilize one or more valves that may be adjusted in response to an operating condition of the vehicle. In one example, an engine may have variable valve timing and/or lift that enables adjustment of cylinder valve operation depending on operating conditions. Specifically, engines may use variable cam timing powered by a hydraulic actuator to vary intake and/or exhaust valve timing relative to crank angle to improve engine performance over a broad range of conditions. However, since hydraulic pressure may not be available during some conditions, these devices may have a spring-biased default position.
However, the inventors herein have recognized disadvantages with these approaches. Specifically, hydraulic pressure may be insufficient during engine start and/or engine stop. As such, the spring-biased system results in the valves being positioned in the default setting during engine starts and/or engine stops, regardless of widely varying starting and/or stopping conditions. For example, the desired valve timing during a warm engine start at sea level may be different than that of a cold engine start at altitude. Likewise, the desired valve setting during an engine shut-down may be different from that of an engine start-up. Further, these issues may be exacerbated in systems having increased engine starting and/or stopping, such as with some hybrid vehicle architectures.
In one approach, the above issues may be addressed by a method of starting an internal combustion engine for a vehicle having at least a hydraulic pump configured to be powered at least partially by a source other than the engine and an adjustable hydraulic actuator configured to be adjusted by hydraulic fluid of the pump, the method comprising during a first start of the engine, operating with the hydraulic actuator in a first position; and during a second start of the engine, operating with the hydraulic actuator in a second position, said second position different from said first position.
In this way, engine start-up over a variety of conditions may be improved, for example, by adjusting operation of intake and/or exhaust valves by hydraulic actuation to account for various conditions.
In another approach, the above issues may be addressed by a method of starting an internal combustion engine for a vehicle having at least a hydraulic pump configured to be powered at least partially by a source other than the engine and an adjustable hydraulic actuator configured to be adjusted by hydraulic fluid of the pump, the method comprising during a shutdown of the engine, operating with the hydraulic actuator in a first position; and during a subsequent start of the engine following said shutdown, operating with the hydraulic actuator in a second position, said second position different from said first position.
In this way, engine shut-downs and start-ups may be improved by enabling the engine to start-up with a different valve operation than was used during engine shut-down.